I've finally made a variation of the popular iPhone 4 Leather Background, for the iPad! It's designed to be subtle and low contrast. Click below to download and let me know what you think in the comments!
UPDATED May 20, 2011
There's also a desktop version of this wallpaper here: Aired Leather Desktop Wallpaper.
UPDATED March 9, 2012
There's a Retina-sized version for the new iPad: Perforated leather background for the new iPad.